With a rise in the standard of living, flat 2D display has hardly satisfied people's increasing need. People start to pursue 3D display with depth perception, which provides a realistic presentation of an object. Since 3D display implemented using a stereoscope was first proposed by Wheatstone in 1838, 3D display has been the subject of vigorous, ongoing research for more than one century and various manners for implementing 3D display have been continually proposed.
Because the two eyes of a person are spaced apart by a certain distance, for a same object, the two eyes respectively view two images slightly different from each other. The two images are fused in the brain, thereby generating depth perception. The principle of 3D display is based on binocular parallax, where parallax images are respectively projected to the right eye and the left eye, ensuring that the left parallax image can be viewed by only the left eye, and the right parallax image can be viewed by only the right eye, such that the viewer can see a stereoscopic image.
The naked-eye 3D display technology has gained increasing attention from researchers, since no visual aid (for example, glasses, a head-mount display, or the like) is necessary for viewing a naked-eye 3D image. Currently, mature naked-eye 3D display technologies include the parallax barrier technology, the lenticular array technology, and the like. However, there are some deficiencies that these technologies cannot overcome, such as low resolution and eyestrain due to a long time of viewing parallax images. With directional backlight technology, in which images are alternatively displayed to the left eye and the right eye, 3D image display with a high resolution can be implemented. The following are examples. As proposed by Yu-Mioun Chu from Taiwan in 2005, 3D display is implemented by directional backlight formed using two wedge-structured light-guide plate, two sets of light sources and one absorption layer, in combination with a fast-switching LCD plate. As proposed by John c. Schultz et al. from Japan in 2009, full-resolution 3D display is implemented using one light guide plate, two LED light sources and a 3D film in combination with a 120 Hz LCD plate. In Chinese patent CN201320143064.8, a directional backlight 3D imaging system is proposed, which uses two projection lenses in combination with a direction 3D optical structure for implementing naked-eye 3D display. The above directional backlight technologies are restricted to a single viewing angle, although high image resolution can be obtained. In view of this, Chin-Hung Ting et al. from Taiwan proposed in 2001 a multi-user 3D film structure applied in a directional backlight system having a single pair of viewing angles, which can implement multi-viewing angle 3D display. Such 3D film has an inverted trapezoidal structure, and is capable of projecting emergent light in three (or more) directions for being viewed by three (or multiple) users simultaneously. In addition, a naked-eye 3D backlight module is proposed in Chinese patent CN201410187534.X, which implements 3D display using one or more sets of LED sequential light sources in combination with convex lenses, polygonal prisms and a parallax barrier. However, the design and high precision machining of the backlight source is difficult technically, and crosstalk of light rays may occurs often.
In international patent of WO2014051624 A1, HEWLETT proposed multi-viewing angle display implemented using waveguide array directional backlight integrated with hybrid lasers, where waveguide arrays are used for guiding red, green and blue light, and directional guiding of light beams are implemented using pixel gratings. With this method, colored multi-view 3D display can be implemented. However, the colored multi-view 3D display is implemented by integrating hybrid lasers into a waveguide array base, which has a high requirement on the fabrication process and has a high cost, and therefore is not conducive to industrial mass production.
In 2013, a multi-view pixel grating directional backlight source is proposed by HEWLETT in a paper in the journal Nature, which can implement, in combination with LCD technology, multi-view naked-eye 3D display. The directional backlight source mainly includes a light guide plate, a collimated light source, and a nano-diffraction grating. Collimated polarized light is transmitted within the light guide plate by means of total reflection, and is incident on a surface of the pixel nano-diffraction grating. Diffraction of light in different viewing angles can be achieved by designing nano-diffraction grating pixels with different periods and different orientation angles. For obtaining true color display, hexagonal light guide plates are adopted in this paper for directional guide of red light, green light and blue light. However, this hexagonal light guide plate does not match with existing flat panel display in displaying manners, and is particularly difficult to be applied to rectangular displays of, for example, smart phones. Moreover, the nano-diffraction grating is fabricated using electron beam exposure, which is inefficient and costly, and is not suitable for preparing a large-sized device.
Therefore, a revolutionary progress can be brought to the naked-eye 3D technology by modifying the above hexagonal light guide plate to a rectangular light guide plate.